1. Field of the Invention
The present invention generally relates to a method for calibrating a UV sensor and a method for controlling UV irradiation for curing a semiconductor substrate using the calibration method.
2. Description of the Related Art
Conventionally, UV irradiation apparatuses have been commonly used for the modification of various processing targets with UV light and the production of substances by means of photochemical reaction. The recent trend of higher integration of devices results in increasingly finer wiring designs and multi-layer wiring structures, which gives rise to a need to reduce the interlayer volume in order to increase the device speed while reducing the power consumption. One method of reducing the interlayer volume is to cure a low-k material through UV irradiation and thereby increase its mechanical strength (for example, U.S. Pat. No. 6,759,098 and U.S. Pat. No. 6,296,909).
In the UV irradiation apparatuses, in order to stably operate UV irradiation processing at a constant illuminance, an illuminance feedback system is employed using a built-in UV sensor. However, the built-in UV sensor is subject to degradation with time due to exposure to UV light, and as a result, illuminance measured by the built-in UV sensor is shifted. Thus, the built-in UV sensor is necessarily calibrated periodically to compensate for the shifted illuminance measurement. Calibration is conducted using measurement data provided by another exterior UV sensor. Namely, a UV unit equipped with the built-in UV sensor is detached from a processing chamber, and placed above an exterior UV sensor, so that the exterior UV sensor is exposed to the UV lamp simultaneously with the built-in UV sensor.
FIG. 1 illustrates such a calibration method. FIG. 1(a) illustrates a schematic view of a conventional UV irradiation apparatus. The UV irradiation apparatus is comprised of a processing chamber 6 and a UV unit 1 mounted thereon. In the processing chamber 6, a heater table 5 is provided for supporting a substrate thereon. In the UV unit 1, a UV lamp 2 is provided for treating a substrate. A built-in UV sensor 3 is also provided in the UV unit 1 to measure illuminance emitted from the UV lamp. An illuminance signal outputted by the built-in UV sensor 3 is fed back to a power control system including a PLC (Power Line Communication) 4 which controls power of the UV lamp, so that even if the UV lamp 2 is degraded and emits less illuminance, the built-in UV sensor 3 catches the reduction of illuminance and the PLC 4 compensates for the reduction of illuminance by increasing power to the UV lamp. As a result, the substrate on the heater table is exposed to UV light with constant illuminance. However, the built-in UV sensor is also subject to degradation with time. Thus, the built-in UV sensor is required to be calibrated after every, e.g., 100 to 300 consecutive hours of irradiation. When calibration is conducted, as illustrated in FIG. 1(b), the UV unit 1 is separated from the processing chamber 6 and mounted on a measuring jig 8 equipped with an exterior UV sensor 7. The exterior UV sensor 7 is then exposed to illuminance emitted from the UV lamp 2, thereby measuring illuminance. The UV unit 1 is separated from the measuring jig 8 and placed back over the processing chamber 6. UV irradiation is then conducted, and the built-in UV sensor 3 is calibrated based on the illuminance measured by the exterior UV sensor 7. After the calibration, UV treatment is resumed.
However, since the above calibration is conducted under different environments, and also since the exterior UV sensor is provided in the measuring jig, the illuminance measured by the exterior UV sensor may not accurately represent the ideal illuminance measured by the built-in UV sensor. Further, such external calibration lowers productivity.
Any discussion of problems and solutions involved in the related art has been included in this disclosure solely for the purposes of providing a context for the present invention, and it should not be taken as an admission that any or all of the discussion were known at the time the invention was made.